What level of complexity can you implement in an application using FastAPI and its ecosystem?

Using FastAPI and its ecosystem, you can implement applications ranging from simple REST APIs to quite complex systems with:

• Data validation and serialization with Pydantic.
• Asynchronous request handling for high performance.
• Authentication and authorization (OAuth2, JWT).
• Integration with databases through ORM (e.g., SQLAlchemy).
• Automatic generation of OpenAPI documentation and Swagger UI.
• Middleware for logging, error handling, and CORS.

An example of a complex application is a microservice with multiple endpoints, asynchronous interaction with databases and external services, as well as a access control system. FastAPI allows for quick development of such solutions with minimal infrastructure costs.